Keratin is the collective name for a family of tough proteins which are found in a number of structures. Keratin is found in hair, feathers, nails, claws, hooves and reptile scales. The keratinized part of the epidermis is known as the stratum corneum. Keratinization occurs when underlying epidermal cells produce and accumulate keratin within their cytoplasm. As they are being pushed towards the surface by the production of new epidermal cells from beneath (only the layer of epidermal cells immediately next to the dermis divide), their organelles and nucleus disappear and they become flattened. The keratin then becomes external from the broken down cells, forming the acellular layer of keratin seen on the surface of mammalian epithelium.